Investigation of Protein Solution Dynamics by Steady-State and Time-Resolved Fluorescence Methods: Protein Oligomer Formation and Ligand Association--Two protein systems are being investigated: (1) the ras p21 oncogene products and (2) the soluble venom (Naja naja & Crotalus adamanteus) and pancreatic (bovine & porcine) phospho- lipase A2s. (1) The oligomeric structure of the ras p21 oncogene proteins and the local conformational dynamics of their guanine nucleotide binding site is being investigated with fluorescently tagged nucleotides. Both global and local environmental parameters are being examined to define the solution oligomer form and the pertinent conformational differences between the GTP- and GDP-forms of the various ras p21 proteins and cancer-causing mutants. Fluorescence lifetimes and dynamic polarization data are being taken. (2) In solution phospholipase A2 (PLA2) isolated from Cobra venom appears to aggregate upon ligand, phospholipid and/or Ca++, while PLA2 from rattlesnake venom remains a dimer and PLA2 from pancreas exists as a monomer. The high degree of sequence similarity and modes of action among these enzymes suggests a common mechanism. The solution structure, the effect of ligands on this structure, and the link between the oligomer and enzyme function are being investigated by fluorescence energy transfer and dynamic polarization.